1. Field of the Invention
The present invention concerns optical transmission. It relates in particular to a space-division switching assembly selectively coupling a first group of N end faces of N first separate optical elements and a second group of P end faces of P second separate optical elements. This space-division switching assembly permits, in particular, broadcast transmission of P programs to N subscribers and thus constitutes an optical program broadcast unit.
2. Description of the Prior Art
Generally speaking, in an optical broadcast unit distributing P programs to N subscribers, N optical fibers are assigned to the transmission of each of the P programs for the N subscribers, the P.times.N resulting fibers being grouped in N groups of P fibers, each assigned to one of the subscribers, whereas an appropriate one of the P fibers in each of the N groups is coupled to the appropriate subscriber fiber so that this subscriber can receive the required one of the P programs available to him.
An optical switch can select one of the P programs for each subscriber.
A mechanical embodiment of an optical switch which provides for obtaining the necessary coupling by deviating a light beam is described in U.S. Pat. No. 4,304,460. This switch comprises a collimator (or focussing) means consisting of a lens and a deviation means consisting of a rotating mirror.
Given the very small dimensions of the optical fibers employed, this switch and, more generally, light deviation type opto-mechanical switches, are of relatively large overall size as compared with that of the fibers and difficult to manufacture if light losses are to be minimised.
Another, also mechanical, embodiment of an optical switch providing for obtaining the necessary coupling by switching a fiber is described in the article "La Commutation optique dans les reseaux locaux de videocommunication" by L. Jeunhomme, published in the Thomson-CSF Revue Technique, volume 14, No 3, September 1982, pages 767 to 785. This solution consists in the use for distribution of the program, facing each subscriber fiber of which the end is equipped with a microlens, of a fiber-carrier barrel consisting of a cylinder with peripheral grooves accommodating the ends of the P so-called program fibers, also equipped with microlenses, and in driving the fiber-carrier barrel by means of a micromotor in order to position the required program fiber opposite the subscriber fiber. In the context of its application to an optical program broadcast unit as specifically envisaged here, in which there are as many switches as subscribers, an embodiment of this kind results in overall dimensions which are prohibitive as compared with those of the optical fibers.
Documents Pat. No. FR-A-2 479 993 and DE-A-3 012 450 also describe mechanically operated optical switches. These switches provide direct or crossover coupling between two incident fibers and two emergent fibers. For this purpose they comprise a mobile intermediate plate disposed between the pair of incident fibers and the pair of emergent fibers, carrying two pairs of intermediate fibers by means of which direct coupling results from a first position of the plate and crossover coupling from a second position of the plate.
These switches permit the implementation of matrix type switching systems between 2n input fibers and 2n output fibers by means of successive associations of switches considered as a basic 2.times.2 switching cell. In the context of application to program broadcasting, such as envisaged hereinabove, these systems would be complex and would not permit the broadcasting of the same program to more than one subscriber at a time.
An objective of the present invention is to provide a space-division switching assembly for selectively coupling end faces of a first group and accesses of a second group for the optical transmission of signals from one of the end faces of one of the two groups to one of the end faces of the other group and, in particular, for the optical broadcasting of P programs to N subscribers, presented in a particularly compact form, using a plurality of switches in the form of modular units possibly of integrated construction and easily reproducible.